1. Field of the Invention
The present invention relates to an electronic imaging apparatus in which control of light quantity is carried out by a system in which the internal transmittance of an optical system is changed instead of a system in which the diameter of an opening of an aperture stop is changed, among conventional systems for controlling quantity of light.
2. Description of the Related Art
In electronic imaging apparatus including the latest digital camera, miniaturization and thinning of it have been progressing. Such miniaturization and thinning are largely owing to miniaturization of an electric circuit and a recording medium.
As a result of the miniaturization of the electric circuit and the recording medium, the proportion of the size to the whole imaging apparatus of the optical system has been increasing relatively. Then, the miniaturization is being made through the miniaturization of an image sensor about an optical system, especially in a zoom lens. For example, the miniaturization and the thinning have been carried out by using mechanical means such as so-called collapsible barrel in which an optical system is pushed out at the time of photographing and is contained inside of the case of an electronic imaging apparatus at the time of carrying it.
However, as the miniaturization progresses, limit in miniaturizing whole optical system in proportion to progress of miniaturization of an image sensor has arisen, because of the limit of physical processing of lens element constituting an optical system, the limit of the strength of mechanism and the limit of manufacture accuracy, etc.
Then, reduction of constituent elements to utmost limit has been attempted by using an a spherical surface and glass material having high refractive index and low dispersion. However, it has also reached at the limit on keeping of basic specification and correction of aberrations.
Therefore, miniaturization of the volume and whole length of an optical system and thinning profile in the depth direction at the collapsed state mentioned above have already reached at the limit in such conventional constitution that optical elements are arranged along a straight line.
Then, as a method of realizing of thin profile to depth direction especially, a method using a reflective surface for bending an optical path in an optical system has been proposed.
It has also been proposed that in order to simplify mechanism, for example, two or more electrochromic elements where the wavelength ranges of the plurality of penetration light differ each other are used by combining them instead of an optical filter or a dichroic mirror, (refer to Japanese Examined Patent Application Publication Toku Kou Hei No.5-27083 and Japanese Unexamined Patent Application Publication No. Toku Kou Hei No.11-160739).